gcd(f_n,f_{n-1})
gcd[f_{n-1},f_n - f_{n-1}]
gcd[(f_n - f_{n-1}), (f_{n-2} - f_{n-1})]
gcd[(f_{n-2} - f_{n-1}),f_{n-3} - f_{n-2})]
gcd[(f_{n-2} - f_{n-3}),(f_{n-4} - f_{n-3})]
.
.
.
gcd(f_2,f_1), where f_2 = 1, f_1 = 1
I assume LateX is not working yet. Not sure if I am on point here or not...